Polyphosphazenes are a broad and well known class of macromolecules based on the repeating unit --(NPR.sub.2)--.sub.n, wherein R can be selected from a wide range of organic or inorganic substituent groups. It has been estimated that by mid 1997 roughly 700 types of polyphosphazenes had been synthesized and characterized, approximately 2000 publications and patents had appeared, and disclosures were appearing at a rate of 170-200 per year on this class of polymers. Polyphosphazenes, J. of Inorganic and Organometallic Polymers, 1992, 2 (2), 197-211.
The predominant route to polyphosphazenes to date has been through the thermal polymerization of hexachlorocyclotriphosphazene (cyclic trimer), also referred to as phosphonitrilic chloride, to poly(dichlorophosphazene) (which has an IUPAC name of poly(nitrilodichlorophosphoranetriyl). This route is illustrated in Scheme 1 below. ##STR1##